1. Field of the Invention
This invention relates generally to an offshore loading system such as a CALM which serves as a single point mooring (SPM) for a shuttle tanker or the like and a product transfer system for transferring hydrocarbon product via an associated product flowline arrangement between a production and/or storage facility and the SPM.
2. Description of Prior Art
In deep water operations, certain operational considerations make it desirable to offload hydrocarbons from a production and/or storage facility by running a pipeline to an offshore loading system, such as a CALM buoy, where a shuttle tanker may be moored and connected to a loading hose for filling its tanks with crude oil. Deep water installations, e.g., in depths greater than about 1000 feet, require that the pipeline be suspended between the production and/or storage facilities, such as a platform or FPSO and the CALM buoy rather than running the pipeline along the sea bed. The pipeline must be submerged at a depth deep enough so as not to interfere with shuttle tanker traffic. A problem exists in connecting the end of the pipeline directly to the CALM buoy, because as the buoy moves up and down and side to side, the end of the pipeline moves with it, and as a result is subject to fatigue failure. The term xe2x80x9cpipelinexe2x80x9d includes steel tubular pipelines as well as bonded and unbonded flexible flowlines fabricated of composite materials.
The problem identified above is inherent in prior offloading deep water CALM buoys which have pipelines attached directly to and supported from a CALM buoy. The pipelines are directly coupled to the CALM buoy such that motions of the CALM buoy are also directly coupled to the pipeline with resulting fatigue damage. Prior systems such as that described in U.S. Pat. No. 5,639,187 have provided a hybrid flowline including rigid (e.g., steel catenary risers) pipelines on the seabed from subsea wells combined with flexible flowlines (e.g., marine hoses) at a submerged buoy which is moored to the seabed by tension leg tether legs. The buoy is positioned at a depth below the turbulence zone of the water. Flexible hoses are fluidly connected to the steel catenary risers at the submerged buoy and extend upward through the turbulence zone to the surface.
Another prior system, described in British Patent GB 2335723 B, attempts to solve the problem identified above by suspending the end of a rigid steel tubular flowline (e.g., the pipeline) by a chain from the offloading buoy and fluidly connecting a flexible hose to the end of the rigid steel flowline below the turbulence zone of the sea. While eliminating a certain level of coupling of wave induced forces to the end of the rigid steel flowline which extends from a production and/or storage facility (FPSO or platform), nevertheless, a sufficient degree of coupling still exists to create a fatigue problem, and possible failure, for the pipeline.
3. Identification of Objects of the Invention
A primary object of the invention is to provide a product transfer system from a FPSO or platform via a pipeline (either rigid or flexible) to an offloading buoy and then to a shuttle tanker while substantially eliminating coupling of wave induced motions of the offloading buoy with the end of the pipeline.
Another object of the invention is to provide a conventional CALM buoy which provides support for a submerged flowline termination buoy for decoupling a submerged pipeline from wave induced motions of the CALM buoy.
Another object of this invention is to provide a submerged flowline termination buoy for support of a submerged pipeline where the buoy is supported by a CALM buoy obviating the need for mooring legs between the flowline termination buoy and the sea floor.
Another object of the invention is to provide a conventional CALM buoy for the product transfer system on which an above-water product swivel is placed so that in-situ servicing of the swivel and CALM buoy can be conducted.
Another object of the invention is to provide an offshore product transfer system that is suitable for use with large diameter, submerged, rigid (e.g., steel) or flexible (e.g., composite) pipelines in deep water.
Another object of the invention is to provide a product transfer system which decouples a submerged pipeline from a surface offloading buoy and its wave induced motions thereby reducing fatigue damage to the pipeline.
Another object of the invention is to provide a product transfer arrangement that allows for optimizing of pipeline diameter and buoyancy, because improved fatigue resistance allows for greater variability in the configuration of the submerged pipeline.
Another object of the invention is to support the flowline in a way that decouples the CALM buoy from the flowline with a resulting low fatigue damage to the flowline at the lowest practical cost.
Another object of the invention is to provide a product transfer arrangement in which the surface offloading buoy can be replaced or repaired easily without disturbing the pipeline from the FPSO or platform with a resulting increase in overall system reliability.
Another object of the invention is to provide a product transfer system that meets the objects described above while employing a conventional surface offloading mooring and hydrocarbon transfer terminal.
The objects identified above along with other advantages and features are provided in the invention embodied in a product transfer system by which a rigid or flexible pipeline from a FPSO or platform or the like extends in the sea above the seabed for about a nautical mile where it terminates close to a CALM buoy, and where it is fluidly coupled to a flexible hose at a Flowline Termination Buoy (FTB) which is supported solely by the CALM below the wave kinematics zone thereby obviating the need for mooring legs between the FTB and the sea floor. The other end of the flexible hose is coupled to the stationary inlet of a product swivel mounted on a stationary portion of a single point mooring offloading buoy such as a CALM. A shuttle tanker is moored to the CALM buoy by a hawser secured to a rotatable portion of the CALM buoy. A hose from the rotatable output of the product swivel extends to the shuttle tanker to complete the product flow path from the (FPSO or platform) to the shuttle tanker.